Medium- or high-voltage electric switches are occasionally installed in electric equipment, such as switching devices for example, in which said switches are incorporated in their corresponding compartment. The compartment of the switch requires using an insulating medium, which can be air or another gas medium, such as, for example, sulfur hexafluoride (SF6), dry air, nitrogen, etc., for the purpose of reducing the distance between phases and thus achieving a compact enclosure that is invariable to external or environmental conditions such as contamination or humidity.
As is known, medium- or high-voltage electric switches are provided for interrupting/cutting off the current circulating through the line at a determined time and can reach the interruption/cut-off value of the apparatus, an electric arc being produced at the time of the separation of the contacts of the switch which can damage them. This is an unwanted phenomenon that has to be extinguished as quickly as possible, given that the arc can destroy the insulations and the contacts, as well as cause an abrupt increase of temperature and pressure which can cause explosions that produce material damages, the formation of toxic gases or even personal injuries. Therefore, the opening/cut-off time is essential.
Another situation that can occur are the closings against short-circuits, i.e., those cases in which a fault is generated when the circuit is closed. In this case, an increase of the current passing through the contacts occurs, reaching several kA, and the contacts are furthermore eroded due to the pre-arc.
In order to limit the wear of the contacts as much as possible, the switch opening operation should be as quick as possible so that the contacts are separated quickly as well. To that end, electric switches use mechanical, hydraulic or electric drives, as well as extinguishing means for extinguishing the arc generated at the time the switch is open, such as for example magnetic blowout systems, static arc lamination and cooling systems, gas fin blowout systems, piston blowout systems, explosive charge detonation systems, systems for ablating a material that can emit a gas to aid in extinguishing the arc, etc.
In the mentioned piston blowout systems, the switch is associated with the piston of a cylinder inside which a gas is located, such that when the switch is open, its movement causes the piston to shift, compressing the gas contained in the chamber of the cylinder, or also referred to as compression chamber, and projecting it on the arc generated at the time of opening the switch, causing it to be extinguished.
These piston blowout arc extinguishing systems have the drawback that when the switch closing operation is performed, the piston must exert considerable force for its retraction since its movement depends on the filling speed of the compression chamber and this filling is done slowly because it is done by taking in gas through the small openings of the chamber. This causes the retraction of the piston to be very slow and the arc that is generated during the closing of the switch can erode the contacts thereof. The gas entering the chamber is also contaminated gas, which can cause unwanted consequences in the next switch opening operation.
In relation to piston blowout systems of this type involving the aforementioned problems, U.S. Pat. No. 5,723,840 and U.S. Pat. No. 5,902,978 can be mentioned as examples.
The solution defined in U.S. Pat. No. 5,723,840 relates to a switch comprising a piston blowout system, which piston is stationary and independent from the moving contact, such that the shifting of the moving contact causes the compression of gas against the stationary piston and consequently the expulsion of said gas through an outlet conduit towards the arcing chamber. Furthermore, in the switch closing operation the compression chamber is filled with gas coming from a suction chamber, the gas passing from one chamber to another through a one-way flow valve comprised in the same piston. In said refreshing of the dielectric medium, the gas coming from the suction chamber is a contaminated gas, because in the opening operation the gases are discharged into said suction chamber, where they are mixed with non-contaminated gas from the exterior, so said mixture of gases with impurities adversely affects the next opening operation.
U.S. Pat. No. 5,902,978 relates to a switch comprising a piston blowout system provided with more than one piston. The movement of these pistons depends on the shifting of the moving contact of the switch, such that said pistons are associated with the moving contact by means of a mechanical transmission such as a cog wheel engaged with the moving contact. The use of the mentioned mechanical transmission involves a complex design consisting of several members, such as, for example, cog wheels, drive transmission members, etc., which in turn involve the drawback of an increase of the size of the switch, whereby the switching devices in which said switch is installed comprise a larger volume, resulting in space problems in the installations. The use of said complex mechanical transmission also involves a higher probability of a malfunction in its operation.
On the other hand, with respect to the problem comprised in piston blowout systems in reference to the retraction speed of the pistons in switch closing operations, the use of more than one piston, as occurs in U.S. Pat. No. 5,902,978, even further affects the shifting speed of the moving contact of the switch in its closing operation, this shifting being slower, so the arc generated between the contacts of the switch has more time to erode such contacts.
In addition to the technical problems considered above in relation to U.S. Pat. No. 5,902,978, it is necessary to mention the insufficiency of means in discharging the gases in when performing the operations of the switch. U.S. Pat. No. 5,902,978 only has one gas outlet in which there is a gas flow deflector. In this sense, in addition to comprising only one gas discharge route, the gas deflector can act as a stopper, blocking the exit of said gases. Consequently, after an operation of the switch the arcing chamber is contaminated for the next operation. On the other hand, this solution defined in U.S. Pat. No. 5,902,978 does not comprise any system for regenerating gas, so the gas used in the next operation will be a gas full of impurities which probably does not aid in extinguishing the electric arc.
Another technical problem comprised in existing piston blowout systems, such as the blowout systems defined in the aforementioned patents, for example, relates to the area in which the electric arc is attacked by means of the blowout, i.e., for example in U.S. Pat. No. 5,723,840 and U.S. Pat. No. 5,902,978 the compressed gas is blown on the arc through an outlet conduit directing the gas on said arc without having any defined point of attack on said arc. By means of this undefined blowout without any point of attack on the arc, the contaminated gases and the plasma generated during the operation of the switch may not be routed to their respective discharge area, a dispersion thereof occurring in the arcing chamber, and consequently, the arc being able to be formed or shifted on the main arc contact and not on the fixed arc contact, causing damages in the main arc contact.
In electric switches the passage of the rated current is generally done in a main circuit provided with at least one fixed contact and at least one moving contact. There are switches which furthermore comprise a secondary or auxiliary circuit provided with contacts, referred to as arc contacts, which stop conducting current after opening the contacts of the main circuit and allow conducting the current before closing the contacts of the main circuit, i.e., the electric arc is formed between said arc contacts. In this sense, some patents defining solutions of this type can be cited, such as for example patents ES2259202T3 and ES2259203T3, which relate to a self-expansion switch comprising in one and the same fixed contact a main contact which allows the rated current to pass and an arc contact for the time of cutting off the current, thus preventing the deterioration of the main contact due to the electric arc generated in cutting off the current. It also allows obtaining a more compact arc chute.
In these patents ES2259202T3 and ES2259203T3, the discharge of the gases caused in the switch cut-off operation are expelled from the arc chute through the inner gap of the moving contact. However, as occurs in the previously mentioned examples, there may be gas and plasma residues caused in the cut-off due to the fact that there is a single discharge route. Consequently, the arc chute is not free of impurities that may jeopardize the next operation. Nor is there any system for regenerating the gas contained in the arcing chamber in these solutions either.
These last two solutions comprise a magnetic blowout system as the arc extinguishing means, such that the fixed contact comprises an electromagnetic coil to rotate the arc. When the contacts separate, the electric arc occurs, the coil is excited and therefore a magnetic field is generated, causing the electric arc to rotate around the arc contact.
The explosive charge detonation systems used as electric arc extinguishing means involve explosive charges which are installed in the arcing chamber of the switches and which, when said charges are detonated by the occurrence of the electric arc, the pressure of the gases generated in said chamber aids in opening the contacts of the switch. In this sense, some patents, such as U.S. Pat. No. 6,107,590 and U.S. Pat. No. 6,252,190, for example, can be cited.
U.S. Pat. No. 6,107,590 relates to a switch comprising an explosive charge detonation system incorporated in the arcing chamber. In the switch opening operation, when the separation between the fixed contact and the moving contact occurs, an arc occurs between them, leading to the detonation of the explosive charge. This detonation causes an overpressure in the arcing chamber which causes the thrust of at least one piston which is integral with the moving contact, such that said generated overpressure contributes to said contact shifting towards the opening of the switch.
In this latter US patent, as occurs in the previous examples, the arcing chamber is not free of contamination after a switch opening operation, nor does it have a system for regenerating the gas contained therein, so the next operation could be jeopardized since there is no pure dielectric medium. The same occurs with the solution described in patent U.S. Pat. No. 6,252,190, which defines a switch comprising an explosive charge for its detonation at the time the arc occurs, aiding the generated overpressure in said detonation to obtain a quicker separation of contacts. As in the previous example, in said patent there is also at least one piston integral with the moving contact which is thrust by the pressure generated in the arcing chamber due to the generation of the gas in the detonation of the explosive charge. This U.S. Pat. No. 6,252,190 also mentions that the switch comprises an ablative material for extinguishing the arc. A portion of the fixed contact of the switch is made of said ablative material, a sliding contact being the one established between the moving contact, specifically the piston, and this portion of the fixed contact, such that due to the arc generated in the separation of the contacts, said consumable portion of the fixed contact releases a gas which aids in extinguishing the arc.
Patent EP0959483 can also be cited as another example of the state of the art, in which the switch comprises extinguishing plates which, when the temperature increases due to the arc generated in the separation of the contacts, said plates release a gas which aids in cooling and extinguishing the electric arc as quickly as possible. This solution does not provide a piston blowout system, but rather the pressure generated in the disconnection causes a stream of gas which aids in cooling and putting out the electric arc.
A device which allows a very quick and efficient extinction of the arc is therefore necessary.